Downhole shutoff tool

ABSTRACT

A downhole drilling valve tool, positioned above the drill bit, which utilizes a ball valve having a through bore for normal flow. The ball valve is operated bidirectionally by a piston driven mechanism between an open position and a closed position. The piston mechanism is responsive to a reference accumulator pressure on a first side and the pressure in the apparatus bore above the ball valve on a second side. Whenever the valve apparatus is lowered at least a minimum distance into the well bore, a pressure relief valve is used to maintain a fixed margin between the flowing bore pressure and the accumulator pressure. Closure of the ball valve occurs when the accumulator pressure exceeds the bore pressure during pump stoppages. The downhole drilling valve tool offers a more wear resistant sealing means, as well as higher pressure operability than conventional downhole check valves.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application, pursuant to 35 U.S.C. 111(b), claims the benefit of the earlier filing date of provisional application Ser. No. 61/743,629 filed Sep. 7, 2012 entitled “Drillstring Shut-Off Valve.”

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates in general to a method and apparatus for controlling fluid flow within a drill pipe. More particularly, the invention relates to a method and apparatus for isolating the interior of a drill pipe from external pressure whenever pumped flow through said drill pipe ceases.

2. Description of the Related Art

The use of check valves in a drill pipe in order to prevent reverse flow is a general practice in petroleum drilling. Use of such valves is necessary in order to avoid the tendency of the normally down flowing drilling fluid to reverse flow during disconnections of the drill pipe from the rig pumps. Backflow from the drill pipe can stow operations and result in loss of expensive drill fluids due to typically higher fluid density in the well annulus compared to the well bore. If the backflow rate is high, hazardous conditions result on the surface, and loss of well control is highly possible.

The check valves used typically are poppet type or flapper type check valves. These conventional valves when flowing always have flow directly contacting their seats and sealing plugs. Both types are notably short lived in drilling applications as a consequence of erosion resulting from the presence of abrasive particles in the drilling fluid and the very high fluid velocities passing through the valves.

There is a critical need for major improvements to the valve means for preventing well backflow during drilling operations for reasons of both safety and economics, particularly for deep wells and offshore wells. Additionally, a critical need exists for longer lived means for controlling well backflow during drilling operations.

SUMMARY OF THE INVENTION

Embodiments of the present invention provide a method and apparatus for isolating the interior of a drill pipe from external pressure whenever pumped flow through the drill pipe ceases. Embodiments of the present invention provide a downhole tool using a ball valve, rotatable between a closed position and a fully open position, that operates in response to differences between the tool bore pressure and the pressure in a reference accumulator. The accumulator is charged downhole to a pressure equal to the highest bore pressure to which the tool has been exposed minus the cracking pressure of a relief valve unidirectionally admitting bore fluid into the accumulator.

One embodiment of the present invention is a downhole shutoff valve for operation in a drillstring, including: a) a housing having a through bore; b) an accumulator positioned within the housing, wherein a gas chamber within the accumulator is selectably chargeable with a gas to create an accumulator pressure, and wherein the accumulator is in fluid communication with a bore pressure present in the bore through a pressure relief valve; c) a ball valve rotatable between a closed position and an open position; d) an axially reciprocable piston exposed to the accumulator pressure on a first side and the bore pressure on a second side; and e) a valve rotational mechanism connected to and operable by the piston, wherein the ball valve is closed by the valve rotational mechanism when the accumulator pressure exceeds the bore pressure and wherein the ball valve is opened by the valve rotational mechanism when the bore pressure exceeds the accumulator pressure.

Another embodiment of the present invention is a downhole shutoff valve including: a) a housing having a through bore; b) a pressure relief valve in fluid communication with the through bore; c) an accumulator positioned within the housing having (i) an accumulator bore, (ii) an accumulator charging port that provides selectable fluid communication between an exterior of the accumulator and a gas chamber to create an accumulator pressure, (iii) a mud chamber in fluid communication with the through bore through a pressure relief valve, and (iv) a separator piston having the mud chamber on a first side and the gas chamber on a second side; d) a ball valve rotatable between a closed position and an open position; e) an axially reciprocable piston movable between a first position and a second position, the reciprocable piston having the gas chamber positioned on a first piston side and a through bore chamber in fluid communication with the through bore positioned on a second piston side; and f) a valve rotational mechanism interconnecting the valve and the piston, wherein when the piston is in the first position the ball valve is in the closed position and when the piston is in the second position the ball valve is in the open position.

Yet another embodiment of the present invention is a downhole shutoff valve including: a) a first module having (i) a first body having a first end, a second end, and a first through bore, (ii) a flow port extending into the first body, wherein the flow port is parallel to and offset from the first through bore, and (iii) a pressure relief valve in fluid communication with the first through bore and the flow port, wherein the pressure relief valve opens when a pressure in the first through bore exceeds a pressure in the flow port by a predetermined amount; b) an accumulator module having (i) a second body having a first module end, a second module end, and a second through bore, wherein the first module end is attached to the first module, (ii) a bore extension tube connected to the first through bore at the second end of the first module and extending into the second through bore, wherein the bore extension tube has a smaller outer diameter than a diameter of the second through bore, (iii) an axially reciprocable separator piston having a first side facing the first module, the separator piston encircling the bore extension tube between an exterior surface of the bore extension tube and an interior surface of the second through bore, (iv) an accumulator charging port providing selectable communication between an exterior of the accumulator module and a gas chamber located between the second through bore and the exterior surface of the bore extension tube on a second side of the separator piston, and (v) a mud chamber in fluid communication with the flow port, the mud chamber located between the second through bore and the exterior surface of the bore extension tube on a second side of the separator piston; and c) a third module having (i) a housing attached to the accumulator module, (ii) a ball valve rotatable between a closed position and an open position, (iii) a third through bore, wherein the third through bore is coaxially aligned and in fluid communication with the first through bore and a bore of the bore extension tube, (iv) a tool bore pressure chamber in fluid communication with the third through bore, (v) an axially reciprocable piston movable between a first position and a second position, the reciprocable piston having the gas chamber positioned on a first piston side and the through bore chamber positioned on a second piston side, and (vi) a valve rotational mechanism interconnecting the valve and the reciprocable piston, wherein when the piston is in the first position the ball valve is in the closed position and when the piston is in the second position the ball valve is in the open position.

The foregoing has outlined rather broadly several aspects of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed might be readily utilized as a basis for modifying or redesigning the structures for carrying out the same purposes as the invention. It should be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and the advantages thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIG. 1 shows the downhole shutoff tool of the present invention in a longitudinal sectional view. The downhole shutoff tool is shown in its precharged configuration prior to its being entered into a well.

FIG. 2 shows a longitudinal sectional view of the housing section of the upper module of FIG. 1.

FIG. 3 shows an exploded view of the upper module of FIGS. 1 and 2.

FIG. 4 shows an exploded view of the pressure relief valve shown in FIG. 2.

FIG. 5 shows an exploded view of the pop off valve shown in FIG. 2.

FIG. 6 shows a longitudinal sectional view of the assembled pressure relief valve shown in FIG. 4.

FIG. 7 shows a longitudinal sectional view of the assembled pop off valve shown in FIG. 5.

FIG. 8 is a longitudinal quarter sectional view of the annular floating separator piston of the upper module.

FIG. 9 is a transverse sectional view taken through the accumulator charging port which shows the elements of the accumulator precharging system in their closed position following precharging.

FIG. 10 is an exploded view showing the components used for the filling of the accumulator housing in FIG. 9.

FIG. 11 shows a longitudinal sectional view of the lower module with the ball valve in its closed position.

FIG. 12 is an exploded view of the internal components of the lower module showing the ball, its seat, its supporting structure, and the actuating piston.

FIG. 13 is a longitudinal sectional view which shows the downhole shutoff tool after it has been lowered into the well and has had drilling fluids pumped through its bore. Drilling fluid from the bore of the tool has entered the upper end of the accumulator module through the pressure relief valve assembly. Because the rig pumps are turned off, the ball is closed due to the bore pressure exceeding the reference accumulator pressure.

FIG. 14 is a longitudinal sectional view which shows the valve in its open, flowing position with the circulation pressure in the drillstring exceeding the reference accumulator pressure.

FIG. 15 is a longitudinal sectional view showing the downhole shutoff tool closed in normal operation downhole when the mudpump is turned off.

FIG. 16 is a transverse cross-sectional view of the pop off valve when the shear pin has been sheared to vent mud from the accumulator chamber during tool retrieval to the surface.

FIG. 17 is longitudinal sectional view when a tubular lockopen tool has been landed in the bore of the drillstring shutoff tool in order to prevent closure of the ball valve.

FIG. 18 is a longitudinal sectional view of the lockopen tool shown in FIG. 17.

FIG. 19 is a longitudinal sectional view of the upper tube of the lockopen tool of FIGS. 17 and 18.

FIG. 20 shows the relationships between the pressures in the accumulator of the tool and the tool bore above the ball valve when the downhole shutoff tool of the present invention is in use.

FIG. 21 is a detail view taken from FIG. 9 showing the closed sealing system for isolating the charged accumulator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention provide a method and apparatus for isolating the interior of a drill pipe from external pressure whenever pumped flow through the drill pipe ceases. For example, embodiments of the present invention provide an automatic valving means for isolating the interior of a drill string from external pressures in a well bore whenever internal pressure in the drill string is reduced below a predetermined amount. The downhole shutoff tool described herein permits drill pipe connections even when the external pressure in the well bore greatly exceeds the hydrostatic pressure within the drill string.

Embodiments of the present invention are shown in the attached figures and are described herein in reference to those figures. Unless otherwise noted, the materials of the downhole shutoff tool are high strength low alloy steel or stainless steel.

Referring to FIG. 1, the downhole shutoff tool 10 of the present invention is shown in a longitudinal sectional view. The righthand end of the tool 10 is the upper end. The downhole shutoff tool configuration in FIG. 1 is its initial arrangement prior to its reference accumulator being charged and the tool being run downhole. When the accumulator is precharged, the configuration is the same, with the piston 62 abutting the lower end of the upper module. The downhole shutoff tool 10 includes three coaxially connected modules 11, 70 and 89 which are joined by pressure containing threaded connections.

The main portion of the upper module 11, seen in detail in FIG. 2, consists of a tubular upper body 12 having transverse ends, a pressure relief valve 24, and a pop off valve 27. FIG. 3 is an exploded view of the entire upper module 11.

The tubular upper body 12 has a through bore 13 with an intermediate lock open sleeve latching groove 14, a tapered upper end female thread 15 and a tapered lower end male thread 20. The thread 15 permits the tool 10 to be sealingly attached to a drill string. At its lower end, the through bore 13 has a lower end counterbore 16. The lower end counterbore 16 in sequential order from its lower end has a lower end female thread 17, a female O-ring groove 18 containing a female O-ring set 19, and a reduced diameter straight portion of the counterbore 16. The female O-ring set 19 consists of an O-ring with two backup rings.

A gundrilled off axis mud port 22 is laterally offset from the axis of the upper body 12 and extends from the lower transverse end of the body to approximately the midlength of the upper body. At its upper end, the off axis mud port 22 intersects the radial pressure relief valve counterbore 23. The pressure relief valve counterbore 23 is coaxially connected to the through bore 13 of the upper body 12 by radial mud entry port 21.

The outwardly opening pressure relief valve counterbore 23 has a frustroconical interior end which radially outwardly increases in diameter from its intersection with the radial mud entry port 21. Extending radially outwardly from the frustroconical interior end, the pressure relief valve counterbore 23 has first straight counterbore section and a female threaded enlarged counterbore section on its outer end. The off axis mud port 22 intercepts the first straight counterbore section of the relief valve counterbore 23.

A vent port 25 extends radially outwardly from its intersection with the off axis mud port 22. The short length vent port 25 intersects the mud port 22 at a position between the radial mud entry port 21 and the transverse shoulder at the upper end of the male lower end thread 20. The outwardly opening pop off valve cavity 26 extends radially outwardly from the vent port 25 and has a coaxial larger constant diameter bore with female snap ring groove 28 near its outer end.

Referring to exploded view FIG. 3, the pressure relief valve 24 with its locking screw 36 and the pop off valve 27 with its retaining snap ring 54 are seen positioned for installation in the pressure relief valve counterbore 23 and the pop off valve cavity 26, respectively. FIG. 4 is an exploded view of the components of the pressure relief valve 24, and FIG. 6 shows a longitudinal cross-sectional view of the assembled valve 24.

Referring to FIG. 2, FIG. 6, and the exploded view in FIG. 4, the components of the pressure relief valve 24 in sequential order from the interior end of the valve are the poppet 30, a set of Belleville spring washers 31, a male O-ring set 32, a spring abutment 34 with a coaxial poppet guide hole 35, and the locking screw 36.

The poppet 30 has a frustroconical interior end with a concentrically positioned elastomeric sealing washer bonded to its frustroconical surface. The frustroconical inner end of the poppet 30 and of the inner end of the pressure relief valve counterbore 23 are sealingly comatable. The outwardly extending upper end of the poppet 30 has a coaxial reduced diameter right circular cylinder which has a slip fit with the poppet guide hole 35 of the spring abutment 34.

The spring abutment 34 is a right circular cylindrical body having a male O-ring groove at its lower end and an enlarged male thread at its upper end. The male O-ring groove of the spring abutment mounts the O-ring set 32, which consists of an O-ring and two backup rings. The O-ring set 32 sealingly comates with the unthreaded portion of the pressure relief valve counterbore 23. The spring abutment 34 is threadedly engaged with the female threads of the pressure relief valve counterbore.

The poppet guide hole 35 is a blind hole which extends coaxially from the inner end of the spring abutment 34. The poppet guide hole 35 is sufficiently deep to permit the Belleville spring washers 31 between the intermediate upwardly oriented transverse face of the poppet 30 and the lower face of the spring abutment 34 to fully flatten if the poppet is unseated by sufficient pressure. The male threaded locking screw 36 is a short right circular cylinder with a central hole and having multiple pin holes offset from the part axis in order to permit a wrench to tighten the screw 36 against the spring abutment 34 sufficiently to ensure both retention of the pressure relief valve assembly 24 and a preselected preload on the springs 31 for biasing the poppet 30 closed.

The pop off valve 27, shown in FIG. 2, a longitudinal sectional view in FIG. 7, and an exploded view in FIG. 5, consists of a carrier 40, a poppet 48, a shear pin 52, a perforated retainer plate 53, and a male snap ring 54. The carrier 40 has a cylindrical outer surface with transverse upper and lower ends and a coaxial stepped upwardly enlarging stepped through bore. On its exterior, the carrier 40 has an intermediate male O-ring groove 41 mounting an O-ring set 44 consisting of an O-ring with two backup rings.

From its lower end, the bore 46 of the carrier 40 has a reduced diameter bore, an upwardly facing frustroconical poppet seat 42 which serves as an abutment for the poppet 48, an intermediate enlarged bore, and a larger upper bore. A through shear pin hole 43 is located on a diameter penetrating the intermediate enlarged bore of the carrier 40. The cylindrical shear pin 52 has a close fit to shear pin hole 43. Multiple regularly spaced radially oriented elongated flow notches 45 which are parallel to the axis of the carrier 40 extend through the carrier cylindrical wall between the larger upper bore and the exterior of the carrier.

The poppet 48 of the pop off valve 27 is a stepped right circular cylinder having a short reduced diameter lower end, a frustroconical downwardly facing shoulder, and an enlarged upper end. A male O-ring groove 41 is located intermediate to the length of the enlarged upper end of the poppet. O-ring set 44 consisting of an O-ring with two backup rings is located in O-ring groove 41. The lower cylindrical section is a close fit to the reduced diameter bore at the lower end of the carrier 40, while the upper cylindrical section is a close slip fit to the intermediate bore of the carrier. The O-ring set 51 seals between the poppet 48 and the carrier 40. The downwardly facing frustroconical shoulder joining the lower and upper cylindrical sections of the poppet 48 has the same angle and orientation as the frustroconical shoulder of the carrier 40.

A shear pin hole 50 which has a close slip fit to a shear pin 52 diametrically penetrates the lower cylindrical section of the poppet 48. When the poppet 48 has its frustroconical face abutted against the corresponding frustroconical face of the carrier 40, the shear pin holes 43 and 50 can be oriented coaxially so that a cylindrical shear pin 52 can temporarily connect the two parts.

The perforated retainer plate 53 is a thin circular disk with a regular array of circular through holes spaced apart from the axis of the disk. The entire pop off valve assembly 27 is contained in the pop off valve cavity 26 by a male snap ring 54.

Referring to the exploded view of FIG. 3, the upper assembly 11 is seen to include on its lower end a bore extension tube 58 and an annular floating separator piston 62. The bore extension tube 58 has a straight through bore 59 and an exterior with a short reduced diameter upper end, a slightly larger upper end male thread 60, and a elongated larger outer diameter lower section 57. The reduced diameter upper end has a close slip fit to the lower end counterbore 16 of the upper body 12 and is sealingly engaged with the O-ring set 19. The male thread 60 is threadedly engaged with the lower end female thread 17 of the upper body 12.

The annular floating separator piston 62 is a short right circular cylindrical section with external male O-ring groove 63 on its outer cylindrical surface and internal female O-ring groove 66 located in its straight through bore 65. O-ring groove 63 contains male O-ring set 64, while O-ring groove 66 contains female O-ring set 67. Each O-ring set 64 and 67 consists of an O-ring and two backup rings. The bore 65 of piston 62 has a close slip fit with the outer diameter 57 of the lower section of the bore extension tube 58, and the O-ring set 67 seals with surface 57 of the bore extension tube.

The accumulator module 70, seen in FIG. 1, mainly consists of an elongated tubular housing 71 having transverse ends, the same outer diameter as the upper body 12, a concentric straight through bore 72, and the female tapered threads 73 and 74 at the upper and lower ends respectively of the module 70. The upper thread 73 is threadedly comatable with the lower end male thread 20 of the upper body 12. At assembly, the transverse upper end of housing 71 sealingly comates with the transverse intermediate downwardly facing external shoulder of the upper body 12 of the upper module 11.

Likewise, the lower female tapered thread 74 of the accumulator housing 71 is threadedly comatable with the upper end male thread 91 of the lower housing 90 of lower module 89. At assembly, the transverse lower end of housing 71 sealingly comates with the transverse intermediate upwardly facing external shoulder of the lower housing 90.

The straight through bore 72 of the accumulator housing 71 has a close slip fit to the outer diameter of the annular floating separator piston 62 of the upper module 11, and O-ring set 64 seals the annular gap between piston 62 and bore 72. Separator piston 62 is able to freely move axially in the annular space between the bore 72 of housing 71 and the outer diameter 57 of bore extension tube 58.

This annular space between the bore 72 of the accumulator housing 71 and the exterior 57 of the bore extension tube 58 serves as a reference accumulator chamber for the downhole shutoff valve 10. The space below the separator piston 62 serves as an accumulator gas chamber 87, while the space above the piston 62 serves as an accumulator mud chamber 88.

As seen in FIGS. 9, 10, and 21, two intersecting ports 76 and 79 for charging the lower accumulator gas chamber 87 are located in a transverse plane approximately one through bore 72 diameter above the lower end female thread 74 at the end of the accumulator housing 71. The radially positioned accumulator charging port 76 penetrates to the bore 72 and has on its inner end a short small diameter first hole penetrating into the bore 72 of the accumulator housing 71. At the outer end of the charging port 76, an outwardly diverging frustroconical shoulder 77 serves as a valve seat for a steel sealing ball 83 which can be forced to sealing mate with the frustroconical shoulder. The diameter of ball 83 is slightly less than that of the outside of the frustroconical shoulder 77.

A first counterbore 78 of charging port 76 is drilled to the frustroconical shoulder 77. Radially outwardly from the frustroconical shoulder 77, the first counterbore 78 has a long straight bore, an O-ring recess for a straight thread/O-ring fitting 85, and an enlarged second section of counterbore to permit the hex head of straight thread/O-ring plug or charging port isolation screw 85 to be fully recessed in the body of the accumulator housing 71. The first counterbore 78 is tapped from the O-ring recess to a point about two bore diameters outwardly from the frustroconical shoulder 77. The hex head charging port isolation plug 85 is sealingly engaged with the threads and O-ring groove of the first counterbore 78.

The clamping screw 84 from its lower transverse end has a first diameter cylindrical section which has a close slip fit to the unthreaded portion of the first counterbore 78. A male O-ring groove containing an O-ring 68 is positioned intermediate to the length of the lower cylindrical section of the clamping screw 84. The O-ring 68 seals the annular gap between the unthreaded portion of the first counterbore 78 and the clamping screw 84. Above the lower cylindrical section, the clamping screw has an enlarged male thread threadedly engagable with the threaded portion of the first counterbore 78 of the accumulator housing 71. A hex Allen wrench socket is positioned on the upper transverse end of the clamping screw 84.

A second port, the small diameter gas fill port 79, extends from the exterior of housing 71 and perpendicularly intersects the accumulator charging port 76 outwardly of the frustroconical valve seat 77 by approximately the diameter of the sealing ball 83. The diameter of the second port near its intersection is approximately the same as that of the inner end of the first counterbore 78 of the accumulator charging port 76. At its outer end, the gas fill port 79 has a tapped counterbore with a straight thread/O-ring groove and recess for the hex head of the straight-thread/O-ring gas fill port isolation screw 86.

The lower module 89 of the downhole shutoff valve 10 is shown in a longitudinal sectional view in FIG. 11 and the internals of the lower module are shown in an exploded view in FIG. 12. Except for the piston assembly 147, the internals of the lower module 89 are housed within the lower housing 90. The main elements of the lower module are the lower housing 90, the valve retainer 100, a ball valve 111 and the ball valve seat 106, the ball rest 116, the lower 120 and upper 129 ball holders, the Lamming arms assembly 134, and the piston assembly 147.

Sequentially from its upper end, the exterior of the lower housing 90 has a transverse upper end, a short reduced diameter right circular cylindrical section 97 with a circumferential male O-ring groove 95, a tapered male thread 91, a transverse sealing face, a long right circular cylindrical external surface, and a transverse lower end. The outer diameter of the upper end cylindrical section has a close slip fit with the bore 72 of the accumulator housing 71.

A male O-ring set 98 consisting of an O-ring and two backup rings is positioned in O-ring groove 95 in order to provide sealing between the cylindrical section 97 of the lower housing 90 and the bore 72 of the accumulator housing 71. From its upper end, the interior of the lower housing 90 has a through bore 94, a larger valve mounting counterbore 93, a straight female retainer thread 96, and a larger tapered lower end female thread 92. The diameter of the retainer thread 96 is slightly larger than the diameter of the counterbore 93. The length of the through bore 94 is equal to approximately 45% of the length of the lower housing 90.

The valve retainer 100, seen best in FIG. 12, is a right circular ring with a straight bore, a male external thread 101, and a short reduced diameter external nose. The thread 101 is comatable with thread 96 of the lower housing 90. On its lower face, the valve retainer 100 has multiple drive pin holes 102 for engagement with spanners.

Abutting the upper end of valve retainer 100 is ball valve seat 106. Ball valve seat 106 has a transverse lower end and a straight through bore which has the same diameter as the bore of the ball valve 111. On its stepped outer cylindrical surface, the larger outer diameter segment of ball valve seat 106 has an O-ring groove mounting a male O-ring set 108 consisting of an O-ring and two backup rings. The larger outer diameter section has a close slip fit to the valve mounting counterbore 93 of the lower housing 90, while the smaller outer diameter section has a close slip to the lower end bores of the lower 120 and upper 129 ball holders. The O-ring set 108 seals between the ball seat 106 and the valve mounting counterbore 93.

A transverse upwardly facing exterior shoulder of the valve seat 106 which abuts the lower ends of the lower 120 and upper 129 ball holders connects the two outer diameter sections of the ball valve seat 106. The upper end of the actual seat 107 of the ball valve seat 106 is spherical and has a close fit to the ball valve 111. An elastomeric sealing element is molded into a central annular groove in the spherical face of the seat 107 to seal between the ball 111 and the metal portion of the valve seat.

The ball valve 111 is best seen in its open position shown in FIG. 12 and its closed position in FIG. 11. The ball valve 111 has a spherical sealing surface with a through hole 115 located on a diameter. Two parallel opposed flats 113 are parallel to and equally offset from the axis of the through hole 115. In the center of each flat 113 is an outwardly extending central pin 112 which is perpendicular to its flat. Each flat 113 has a rectangular cross-section camming groove 114 spaced a short distance from its central pin and extending radially outwardly 45° from the axis of the through hole 115. Each camming groove 114 exits through the spherical outer surface of the ball valve 111. The camming grooves are symmetrical about the midplane between the flats 113 of the ball.

The ball rest 116, seen in FIGS. 11 and 12, is formed from an axially short, right circular cylindrical piece with a straight through bore 118, a spherical lower end, a transverse upper end, and a stepped outer diameter. The bore of the ball rest 116 is the same as the through bore 115 of the ball valve 111. The spherical lower end is a close fit to the spherical surface of the ball valve 111. On its upper end, the ball rest 116 outer diameter has a larger section which extends for approximately half of the axial length of the ball rest. This larger section is a close slip fit to the valve mounting counterbore 93 of the lower housing 90. The larger cylindrical outer surface of the ball rest 116 is interrupted by two mirror image flats 117 parallel to the axis of the part and having a separation equal to the smaller outer diameter. This separation distance of the ball rest flats 117 is equal to the separation distance of the flats 113 on the ball 111.

The lower ball holder 120, best seen in FIG. 12, is made from a half cylindrical part having a constant outer diameter which has a close slip fit to the valve mounting counterbore 93 of the lower housing 90. The upper end of the bore of the half cylinder has a radius which is a close slip fit to the smaller cylindrical outer surface diameter of the ball valve seat 106. A rectangular cut transverse to the longitudinal midplane of symmetry of the source half cylinder and having two sides parallel to the axis of symmetry of the half cylinder is made with one edge a short distance from the lower end of the half cylinder and the opposed edge about 40% of the length of the lower ball holder 120 from the transverse upper end of the part. The side 121 of the rectangular cut farthest from the part axis of the lower ball holder 120 is tangent to the larger diameter bore of the source half cylinder and extends to the bore diameter transition of the source half cylinder.

A ball pin hole 122 perpendicular to the flat side 121 of the cut and located on the longitudinal midplane of the lower ball holder 120 is a close fit to a central pin 112 of the ball valve 111 and serves as a support for the ball. An elongated rectangular slot 123 offset from the longitudinal midplane of the lower ball holder 120 and normal to the flat interior side 121 of the rectangular window cut penetrates to the outer cylindrical surface of the lower ball holder 120. This slot 123 offers lateral guidance to the lower camming arm 141 of the camming arm assembly 134. The upper end of the slot 123 extends to within approximately a quarter diameter of the lower ball holder 120 and the slot lower end is located at approximately the lower end of the rectangular cut in the ball holder.

A drilled and tapped stroke limiter hole 124 perpendicularly intercepts the lower transverse end of the lower ball holder 120 and mounts a first stroke limiter set screw 125 which is used to limit the downward stroke of the lower arm 141 of the camming arms 134. A similar but longer drilled and tapped hole 124 coaxial with the first hole 124 penetrates both the upper end of the lower ball holder 120 and the upper end of the slot. This second hole 124 mounts another screw 125 which serves to limit the upward stroke of the lower camming arm 141 of the camming arm assembly 134.

The upper ball holder 129 is a mirror image of the lower ball holder 120 and also uses the same stroke limiter set screws 125 to limit travel of the upper camming arm 139.

The camming arm assembly 134 consists of an elongated thin walled right circular tubular body 135 having a male thread 137 at its upper end and a radial through hole 136 spaced a short distance below the thread 137. At its lower end, a pair of mirror image external arms 139, 141 laterally offset from the longitudinal axis of the tube extend downwardly. The opposed inner faces of the arms are parallel and are separated by a distance slightly larger than the separation of the flats 113 of the ball valve 111. The outer faces of the arms 139, 141 opposed to their inner faces are cylindrical and are a slip fit to the valve mounting counterbore 93 of the lower housing 90.

The lateral sides of the camming external arms 139, 141 are parallel and are a slip fit to the camming arm guide slots 123 of the lower 120 and upper 129 ball holders when the ball holders are assembled around the camming arms assembly 134. The difference between the length of the camming external arms 139, 141 and the tips of the stroke limiter screws 125 at the interior ends of the camming arm guide slots 123 of the lower and upper ball holders determines the stroke travel of the camming arms assembly for rotating the ball valve 111. The lower screws 125 are adjusted to ensure full alignment of the ball through bore 115 with the axis of the tool 10 when the valve 111 is opened. Likewise, the upper screws 125 are adjusted to ensure the elastomer 107 of the seat 106 fully seals on the closed ball.

Coaxial holes 140, 142 respectively at the lower ends of the individual camming arms 139, 141 and normal to the longitudinal midplane of the camming arms assembly each serve to mount an inwardly extending camming pin 144. The camming pins 144 are short with a larger diameter portion which has a slip fit to a camming slot 114 on the ball valve 111 and a smaller diameter portion which has an press fit with the mounting holes 140 or 142 on the lower end of the camming arms 139, 141.

The piston assembly 146, seen in FIGS. 11 and 12, consists of piston 147, a male O-ring set 149, and two female O-ring sets 152 and 154. The piston 147 of the piston assembly is a right circular cylindrical body of revolution with transverse ends. The upper exterior portion 148 of piston 147 has a reduced diameter extending approximately half of the length of the part, while the lower exterior portion has a close slip fit to the through bore 72 of the accumulator housing 70. An annular male O-ring groove 150 located on the larger diameter exterior cylindrical surface of the piston 147 mounts a male O-ring set 150 consisting of an O-ring with two backup rings. The male O-ring set seals between the piston 147 and the bore 72 of the accumulator housing 70.

The through bore of the piston 147 has from its upper end a straight counterbore 156 extending about half of the length of the piston. The diameter of the counterbore 156 is a close slip fit to the outer diameter of the lower tube surface 57 of the bore extension tube 58. A first female O-ring groove 153 houses a female O-ring 152 set composed of an O-ring with two backup rings to provide dynamic sealing between the piston assembly 147 and the lower end of the bore extension tube 58.

The central portion of the bore of piston 177 has a reduced diameter with a female thread 151. The female thread 151 is threadedly comatable with the male thread 137 at the upper end of the camming arm assembly 134. Below the female thread 151 of piston 147 is a short counterbore which is a close slip fit to the outer diameter of the tubular body 135 of the camming arm assembly 134. A second female O-ring groove 155 in the lower counterbore mounts a static O-ring set 154 consisting of an O-ring and two backup rings for sealing between the piston 146 and the camming arm assembly 134.

A tool bore pressure chamber 158 is created in the assembled tool 10 between the lower end of the piston assembly 147 and the upper end of lower housing 90 of the lower module 89. The tool bore pressure chamber 158 is bounded on its outer diameter by the through bore 72 of the accumulator housing 71 and on its inner diameter by the outer diameter of the tubular body 135 of the camming arm assembly 134.

Pressure from the through bore of the camming arms assembly 134 and, hence, the bore of the entire downhole shutoff valve 10 is communicated to the tool bore pressure chamber 158 through the communication port 136 of the camming arms assembly. This bore pressure is applied to the lower end of the piston assembly 147. The pressure in the gas chamber 87 of the accumulator module 70 acts on the upper end of the piston assembly.

In some cases, it is advisable for operational reasons to lock open ball 111 of the downhole shutoff valve 10 either before or after the tool has been run downhole. FIGS. 17, 18, and 19 show a possible means for accomplishing the locking open of the ball valve 111 of the downhole shutoff valve 10.

Referring to FIG. 18, the details of a pumpdown lockopen tool 160 can be seen. The lockopen tool consists of a main tube 161, a guide nose 162, a middle tube 164, a shear pin 170, an external latch ring 171, a set of four travel limiting screws 172, a frangible disk 173, and an upper tube 176.

FIG. 17 shows the tubular lockopen tool 160 which has been inserted inside the drillstring at the surface and pumped down to land in a position to prevent the ball valve 111 from closing. The pumping causes the ball valve 111 to open, permitting the downwardly traveling lockopen tool 160 to insert its main tube 161 through the open bore of the tool 10 and the bore 115 of the ball. When the lockopen tool 160 has moved sufficiently downwardly, it latches its external latch ring 171 into the lockopen sleeve latching groove 14 in the through bore 13 of the upper body 12. The pumping down of the lockopen tool 160 is possible because its bore is temporarily blocked by a thin frangible disk 173.

Referring to the longitudinal sectional view of the lockopen tool 160 in FIG. 18, the round main tube 161 is relatively long, with a pointed stabbing guide nose 162 composed of three plates welded into its lower end, as seen in FIG. 18. The outer diameter of the main tube 161 is a loose slip fit to the through bore 115 of the ball 111. At its upper end, the main tube is coaxially welded to the middle tube 164.

The middle tube 164 is only slightly longer than its outer diameter. The middle tube 164 at its lower end has the same inner and outer diameters as the main tube 161. The exterior of the middle tube has a short lower section, a upwardly facing transverse shoulder, and then a reduced diameter cylindrical neck 165 at its upper end. The bore of the middle tube from the bottom end inwardly converges and then has a constant diameter extending to the upper transverse end of the part.

The upper portion of the middle tube 164 has a relatively thin wall. Just below its upper end, the middle tube has four guide slots 167 circumferentially equispaced and elongated in the axial direction of the part. A radial drilled and tapped shear pin hole 166 to accommodate a shear pin 170 is spaced upwardly from the intermediate outer transverse shoulder of the middle tube 164.

An external latch ring 171 has a thin wall with a short axial length and relatively large external chamfers on its upper and lower sides. The external latch ring outer diameter is the same as the outer diameter of the lock open sleeve latching groove 14 of the upper body 12 of the upper module 11, and the axial length of latch ring 171 is such that it has a loose fit in the groove 14. The external latch ring 171 has a small section of its circumference removed in order to permit it to be radially contracted in order to pass through the through bore 13 of the upper body 12 of the upper module 11. The material of the latch ring 171 is hardened steel in order to permit it to be compressed in the through bore of the upper body without experiencing permanent distortion.

The upper tube 176 of the lockopen tool 160 is shown in a longitudinal sectional view in FIG. 19. The upper tube 176 has a transverse lower end external shoulder 179, a lower counterbore 177 which has a slip fit with the reduced diameter neck 165 of the middle tube 164, a downwardly facing inwardly extending transverse shoulder, and a reduced diameter upper bore which contains an elongated intermediate internal latch groove 178. The internal latch groove 178 is configured to accept an industry standard wireline retrieval tool. The length of the lower end counterbore is slightly more than the length of the reduced diameter neck of the middle tube.

On its exterior, the upper tube 176 has from its lower end a short first reduced diameter ring expander section 179 which has a diameter equal to or slightly less than the diameter of lockopen sleeve latching groove 14 of the upper module 11 minus the difference in outer and inner diameters of the external latch ring 171. Adjacent to the ring expander section 179 on its upward side is a short latch ring recess 180. The diameter of the latch ring recess 180 is slightly less than the inner diameter of the through bore 13 of the upper body 12 of the upper module minus the difference of the outer and inner diameters of the latch ring 171. The length of the latch ring recess 180 is slightly more than the axial length of the latch ring 171. A chamfer joins the ring expander section 179 and the latch ring recess 180.

The relatively long external cylindrical surface 183 of the upper tube 176 is located immediately above the latch ring recess 180. An outwardly extending downwardly facing transverse shoulder joins the external cylindrical surface 183 of the upper tube 176 to the latch ring recess 180. The diameter of the external cylindrical surface 183 is a loose slip fit to the through bore 13 of the upper body 12 of the upper module 11. At the upper end of the upper tube 176, a short outwardly and upwardly extending inclined external landing shoulder 184 is configured to abut the transition from the upper end female thread 15 to the through bore 13 of the upper body 12 of the upper module 11.

Four circumferentially equispaced drilled and tapped radial screw holes 181 in a common transverse plane of the upper tube 176 penetrate the tube a short distance upwardly of the transition between the latch ring recess 180 and the external cylindrical surface 183. Each hole mounts an inwardly projecting travel limiting screw 172. The travel limiting screws 172 are half dog point set screws with short reduced diameter cylindrical tips. The tips of the screws 172 are engaged in the guide slots 167 of the middle tube. When the lockopen tool is in its assembled running position shown in FIG. 18, the tips of the screws 172 are positioned in the lower end of the guide slots 167.

The frangible disk 173 is an axially thin cylindrical member made either from a brittle material of limited strength or a metal disk scored to provide lines of failure. When the frangible disk is exposed to high transverse pressure, it will rupture. The diameter of the disk 173 is a close slip fit to the lower counterbore 177 of the upper tube 176.

A radial drilled and tapped shear pin hole 182 is match drilled and match tapped with the upper tube 176 and the middle tube 164 assembled to abut each other with the travel limiting screws 172 and the frangible disk 173 installed as shown in FIG. 18. The shear pin hole 166 of the middle tube 164 is produced by this operation. The threaded brass shear pin 170 has a screw slot in its upper end and is threadedly engaged with both the shear pin hole 182 of the upper tube 176 and the shear pin hole 166 of the middle tube 164.

The lockopen tool is assembled by placing the frangible disk 173 at the upper end of the middle tube and then abutting the shoulder at the upper end of the lower counterbore 177 of the upper tube 176 against the disk. At that point, the travel limiting screws are engaged both through the screw holes 181 of the upper tube 176 and the guide slots 167 of the middle tube 164. Following this, the shear pin 170 is engaged in the drilled and tapped shear pin hole 182 of the upper tube 176 and the shear pin hole 166 of the middle tube 161.

OPERATION OF THE INVENTION

The drillstring shutoff tool in service will be mounted near the lower end of a drillstring, typically very close to the drill bit. When the drillstring shutoff tool 10 of the present invention is initially assembled prior to being precharged and mounted in a drillstring, it has the configuration shown in FIG. 1. The floating separator piston 62 may possibly be spaced apart from the lower end of the upper body 12, but after the accumulator module 70 gas chamber 87 is precharged with nitrogen, the piston will be abutted against the lower end of the body 12 by the retained nitrogen pressure.

The nitrogen precharge is introduced into the accumulator gas chamber 87 in the following manner. First, the gas port isolation plug 86 is removed and a nitrogen source is connected to the threaded counterbore 80 of the gas fill port 79. Following this, the charging port isolation plug 85 is removed and the clamping set screw 84 is backed off sufficiently to allow the sealing ball 83 to lift from its seated position on the valve seat 77. At this point, pressurized nitrogen at a preselected regulated pressure can flow into the accumulator gas chamber 87. Following its filling to a desired pressure, the accumulator gas chamber is again isolated by reversing the procedure for admitting gas into the accumulator.

The amount of nitrogen precharge in the accumulator is predetermined by the expected range of operational depths for the tool 10. Typically, the precharge pressure will range from a few atmospheres to approximately 1500 psi. The precharge pressure is limited to be at least slightly less than the anticipated initial downhole hydrostatic pressure at the bottom of the drillstring minus the cracking pressure of the pressure relief valve 24. However, as a practical matter, it is desirable to keep pressures to which operational personnel are exposed at fairly low values.

The pressure relief valve assembly 24 has its Belleville spring washer set 31 preloaded so that its poppet 30 will open for a certain differential pressure across the valve. Normally, this differential pressure will be on the order of a few hundred psi. When the shutoff tool 10 is lowered into a well, the ball initially will be shut, as shown in FIG. 1. Normally, the drillstring is filled with drilling fluid either intermittently as it is being lowered into the well or when it has reached the bottom of the well. This produces hydrostatic pressure in the bore of the drillstring at the elevation of the tool 10. When this hydrostatic pressure exceeds the opening pressure of the relief valve assembly 24, that valve opens and admits drilling fluid to the off axis mud port 22. The pressure relief valve 24 does not permit reverse flow.

The resultant flow through the relief valve 24 then is enabled to enter the space between the separator piston 62 and the bottom end of the upper body 12. When the hydrostatic pressure at the level of the tool minus the cracking pressure of the relief valve 24 exceeds the accumulator precharge pressure, the separator piston 62 will begin to be displaced downwardly thereby establishing an accumulator mud chamber 88, as shown in FIG. 13. FIG. 15 shows how the separator piston 62 is displaced downwardly when the tool 10 has reached its drilling depth.

As the shutoff tool is lowered into the well in the usual well situation, at the depth of the tool, the external hydrostatic pressure will be equal to or will exceed the hydrostatic in the bore of the tool. Since the pop off valve 27 is thus not experiencing a positive pressure differential between the pressure in the off axis mud port 22 and the exterior of the tool, it remains closed.

When the tool reaches the bottom of the well, the drillstring is completely filled with drilling fluid using the mud pumps. This results in sufficient drilling fluid entry into the relief valve 24 so that the accumulator pressure increases and becomes substantially the same on both sides 87 and 88 of the separator piston 62. The retained accumulator pressure at that time is equal to the hydrostatic bore pressure in the bore of the tool 10 minus the cracking pressure of the relief valve 24. The increased pressure in the accumulator chambers 87 and 88 results in substantial downward displacement of the separator piston 62, as shown in FIG. 15.

Since the drillstring shutoff tool 10 is intended for use in drilling, in service a drill bit having restrictive flow nozzles will be installed below the tool 10. When the drill rig mud pumps are running and causing fluid to flow down the drillstring at a typically high flow rate, a significant pressure drop develops across the bit flow nozzles. Thus, when the rig is pumping, a differential is developed between the pressure external to the drillstring and the internal pressure in the drillstring and the tool 10. For this situation at the depth at which the tool is located, the pressure in the drillstring is higher than the combined hydrostatic and flow induced pressure in the well annulus between the drillstring and the well bore.

In the active drilling situation, the pressure in the bore of the drillstring shutoff tool 10 is equal to the hydrostatic pressure plus the mud pump output pressure minus the flow induced pressure losses inside the drillstring between the mud pump and the tool. The pressure in the drilling fluid inside the accumulator is essentially the combined drilling pressure at the level of the tool minus the cracking pressure of the relief valve 24. When the mudpumps are being stopped, the pressure in the bore of the tool also is being reduced, but the volume of drilling fluid in the accumulator mud chamber 88 cannot reduce, since the relief valve 24 will not exhaust fluid.

The Belleville spring washer set 31 is selected and preloaded to carefully control the opening differential pressure of the pressure relief valve assembly 24. The relief valve 24 opening pressure is selected to be a fraction of the anticipated pressure drop across the bit nozzles for the drilling assembly. Normally, the drilling rig mud pumps are run at or near their maximum speed, as the drilling rate is closely related to the flow rate through the bit.

Relatively low forces on piston assembly 146 are required to operate the ball valve 111, so by way of example, the opening pressure for the pressure relief valve assembly 24 would be selected to be in the range of 20% to 60% of the minimum pressure drop across the bit nozzles with the pumps running at full speed during a run of the downhole shutoff valve 10. The lower limit of the opening pressure differential for the pressure relief valve 24 is selected to ensure that adequate closing force is available to overcome frictional forces resisting closure of the ball valve 111. Use of a relatively lower opening pressure for the pressure relief valve 24 avoids excessive fluid erosive wear on the ball 111 during opening and closing.

FIG. 20 illustrates the relationships between the pressure retained in the accumulator and the pressure in the bore during drilling. The pressure retained in the accumulator chambers 87 and 88 is indicated by a dashed line, while the pressure in the through bore of the drilling shutoff tool is illustrated by a solid line. For simplicity, it is assumed that the bore of the drill string is continually filled as the tool 10 is lowered into the well. Additionally, the drilling fluid density is assumed constant, the effects of temperature change on the accumulator gas pressure are ignored, and the pumps are always run at the same speed. The relatively small changes in accumulator gas chamber pressure 87 as the piston 146 attached to the camming arm assembly 134 strokes are also ignored herein for simplicity.

Initially, no drilling fluid enters the accumulator through the pressure relief valve 24. This is because the accumulator gas chamber pressure 87 plus the cracking pressure of the pressure relief valve 24 initially exceeds the hydrostatic pressure of the drilling fluid in the drillstring. However, when the hydrostatic pressure at the depth of the lowering tool exceeds the accumulator pressure plus the cracking pressure of the relief valve 24, drilling fluid will enter the accumulator. At this point, the accumulator pressure curve in FIG. 20 begins to increase from its precharged value. In response to the positive pressure differential between the bore of the tool and the accumulator chamber 87, the piston 146 and its attached camming arms 139, 141 move upwardly. The camming pins 144, mounted on the camming arm assembly 134 and engaged in the camming grooves 114, apply an off axis force to the ball 111, causing it to rotate to its open position, thereby permitting flow through the drill bit and into the well bore.

When the mud pumps of the rig are first turned on with the drillstring filled, assuming that the pumps are run at the same speed each time, the pressure in the bore of the tool increases by approximately the same amount, but the accumulator pressure always lags by the amount of the relief valve 24 cracking pressure when the mud pumps are running. Relatively minor reductions with increase in depth in the circulating bore pressure for the tool due to flow losses in the drillstring are not treated here for simplicity. Whenever the rig pumps turn off, the pressure in the bore of the tool decreases to the hydrostatic pressure of the drilling fluid column in the drillstring due to closure of the ball valve 111 of the tool 10.

However, as long as the differential between the flowing pressure and the nonflowing pressure at the exterior of the tool 10 when the pumps are stopped does not exceed the opening pressure of the pop off valve 27, the difference between the accumulator pressure and the flowing pressure in the tool bore is constant. When the drillstring is filled and the pumps are turned on, the pressure in the tool bore increases to a point at which the pressure communicated through the communication port 136 of the camming arms to the tool bore pressure chamber 158 will exceed the pressure in the accumulator gas chamber 87. This pressure differential produces an upwardly acting differential pressure acting on the piston 146 attached to the camming arm assembly 134, thereby causing the ball valve 111 to open.

As the rig pumps slow down in the process of stopping, the tool bore pressure drops below the retained pressure in the gas chamber 87 of the accumulator 70. The piston assembly 146 attached to the camming arm assembly 134 is exposed to the pressure of the gas chamber 87 on its upper side and on its lower side to the tool bore pressure communicated through the communication port 136 to the tool bore pressure chamber 158. In response to the pressure differential, the piston 146 and its attached camming arm assembly 134 move downwardly. The camming pins 144, mounted on the camming arm 139, 141 and engaged in the camming grooves 114, apply a downward off axis force to the ball 111, causing it to rotate to its closed position.

When the drilling shutoff valve 10 is being withdrawn from the well, the hydrostatic pressure decreases, but the pressure in the accumulator chambers 87 and 88 is trapped until the shear pin 52 of the pop off valve 27 shears, releasing the drilling fluid retained in the accumulator mud chamber 88. The shear pin 52 shears in response to sufficiently high forces on the poppet 48 of the pop off valve 27 due to the pressure differential between the accumulator mud chamber 88 and the exterior of the tool. The pressure of the nitrogen in the accumulator gas chamber 87 then urges the floating separator piston 62 upwardly until it abuts the lower end of the upper body 12. No nitrogen is released at this point, so the nitrogen pressure stays the same except for temperature induced variations as the drilling shutoff tool is pulled from the well.

The pop off valve 27 is always exposed to the pressure in the off axis mud port 22 and hence the pressure on the upper side of the separator piston 62 in the accumulator 70. The accumulator pressure directly acts on the cross sectional area of the outer end of the valve poppet 48. When the outwardly acting differential pressure force on the poppet 48 exceeds the shear strength of the shear pin 52, the poppet shifts radially outwardly until it abuts the perforated retainer plate 53. The shifting of the poppet permits drilling fluid on the upper side of the separator piston 62 to be forced past the poppet from the accumulator mud chamber 88, thereby dropping the pressure in the accumulator to its initial precharge pressure.

The lockopen tool 160 uses latching of its external latch ring 171 to retain the tool 160 in position to prevent closure of the ball 111. As the downwardly moving lockopen tool 160 enters the open ball 111, the external latch ring 171 is forced to constrict its outer diameter by being forced into the through bore 13 of the upper body 12 of the upper module 11. Internal forces acting on the compressed latch ring 171 urge it radially outward so that it can recess in the latch ring recess 180 of the upper tube 176 of the lockopen tool. When the lockopen tool moves sufficiently downwardly, the radially compressed latch ring 171 will expand and engage in the latching groove 14 to trap the lockopen tool 160 so that it prevents closure of the ball valve 111.

If a force shoves the lockopen tool upwardly, the latch ring 171 will slide both to abut the upwardly facing shoulder of the middle tube 164 and to be supported radially by resting on the outer diameter of the lower end external shoulder 179. In this position, there is no force on the shear pin 170 and the latch ring cannot collapse sufficiently to release the lockopen tool.

Retrieval of the lockopen tool 160 is possible by applying upward tension on the upper tube 176. This tension can be applied by latching a industry standard wireline retrieval tool into the internal latch groove 178 of the upper tool and then exerting sufficient upward pull on the wireline to shear the shear pin 170.

Prior to the shearing out of the latched lockopen tool 160, the pull of the wireline produces a reactive force between the latch ring 171 and the groove 14 in the upper module 11. This causes the latch ring 171 to bear on the intermediate upwardly facing transverse shoulder of the middle tube 164. When the resultant shear force in the shear pin 170 is sufficient to fail the pin 170, a gap opens up between the lower end of the upper tube 176 and the upwardly facing intermediate shoulder of the middle tube 164. The radial inward forces applied to the latch ring 171 by its abutting against the upper end of the latching groove 14 of the upper module 11 cause the ring to collapse sufficiently to permit lockopen tool retrieval. The travel limiting screws 172 prevent separation of the middle tube 164 and the upper tube 176, so that the lockopen tool 160 remains an integral unit during retrieval.

The lockopen tool 160 can be utilized to hold the downhole shutoff valve 10 open by positioning the lower end of the main tube 161 through the bore of the open ball 111. This can be done in either of two ways. The first way is by assembling the downhole shutoff valve 10 prior to its being precharged with nitrogen with its ball initially open and the main tube of the lockopen tool 160 inserted through the bore 115 of the ball 111. The external latch ring 171 of the lockopen tool 160 must be engaged in the latching groove 14 of the upper body 12 and the frangible disk 173 omitted from the assembled lockopen tool in this case. This permits the downhole shutoff valve 10 to be run into the well in an open condition so that the drillstring will freely flood without pumping fluid into the drillstring. For this first method of operation, the lockopen tool must be retrieved by wireline to enable normal downhole shutoff valve operation.

The second method for using the lockopen tool 160 is to pump it into place downhole. In this situation, the ball 111 of the downhole shutoff valve 10 is open due to the pump flow, so that the guide nose 162 and the main tube 161 can freely enter the bore 115 of the ball and thereby prevent ball closure. When the lockopen tool 160 has latched into the bore of the downhole shutoff valve 10, further pumping will rupture the frangible disk 173. As a result, bidirectional flow is then possible through the locked open drilling shutoff valve 10, and the drillstring can freely drain as it is retrieved from the well.

ADVANTAGES OF THE INVENTION

The downhole shutoff valve of the present invention provides a more reliable means of preventing backflow into a drillstring when the rig mud pumps are stopped. Conventional flapper type or poppet type check valves have proved to be unreliable in downhole drilling service.

The downhole shutoff valve disclosed herein experiences far less wear than conventional downhole check valves because, unlike the case for those valves, the valve seat and sealing surface of the valve are not exposed to erosive flow.

The accumulator precharging pressure is relatively low, and the venting of the pop off valve of the retrieved downhole shutoff valve prevents exposure of personnel to the pressures higher than the precharging pressure of the tool. Another advantage of the present invention is that it automatically compensates for changes in its operating depth.

A further advantage of the tool is that an accessory tool, the wireline run and retrieved lockopen tool disclosed herein, can be used to avoid the necessity of filling the drillstring prior to initial operation downhole. Additionally, the pump in installation of the lockopen tool permits pulling the drillstring with fluid retained in the pipe.

The construction and assembly/disassembly of the downhole shutoff valve are relatively simple. Conventional materials used for mechanical oilfield downhole tools are also used for the downhole shutoff valve. These and other advantages will be obvious to those skilled in the art.

As well may be understood by those skilled in the art, certain features of the downhole shutoff valve of the present invention may be modified without departing from the spirit of the invention. By way of example, the ball valve could be operated by a rack and pinion arrangement. The pressure relief valve and the pop off valve could be connected to the accumulator by separate flow paths. The accumulator could be recharged through a check valve without using a separate, intersecting flow path. The downhole shutoff valve could be operated without using a lockopen tool. The configuration of the latching and retrieval means of the lockopen tool could be altered. However, these changes would not depart from the spirit of the invention. 

What is claimed is:
 1. A downhole shutoff valve for operation in a drillstring, including: a) a housing having a through bore; b) an accumulator positioned within the housing, wherein a gas chamber within the accumulator is selectably chargeable with a gas to create an accumulator pressure, and wherein the accumulator is in fluid communication with a bore pressure present in the bore through a pressure relief valve; c) a ball valve rotatable between a closed position and an open position; d) an axially reciprocable piston exposed to the accumulator pressure on a first side and the bore pressure on a second side; and e) a valve rotational mechanism connected to and operable by the piston, wherein the ball valve is closed by the valve rotational mechanism when the accumulator pressure exceeds the bore pressure and wherein the ball valve is opened by the valve rotational mechanism when the bore pressure exceeds the accumulator pressure.
 2. The downhole shutoff valve of claim 1, wherein whenever the accumulator pressure is greater than a pressure exterior to the downhole shutoff valve by a predetermined margin, a pop off valve opens and releases to the tool exterior an excess of the accumulator pressure over the pressure external to the downhole shutoff tool.
 3. The downhole shutoff valve of claim 2, wherein the pop off valve consists of a carrier and a poppet closed with a shear pin and opened by shearing the shear pin.
 4. The downhole shutoff valve of claim 1, wherein the through bore has a latch groove.
 5. The downhole shutoff valve of claim 4, further including a lockopen tool that selectably interacts with the latch groove to position the lockopen tool in the through bore to prevent opening or closing of the valve.
 6. A downhole shutoff valve for use in a drillstring including: a) a housing having a through bore; b) a pressure relief valve in fluid communication with the through bore; c) an accumulator positioned within the housing having (i) an accumulator bore, (ii) an accumulator charging port that provides selectable fluid communication between an exterior of the accumulator and a gas chamber to create an accumulator pressure, (iii) a mud chamber in fluid communication with the through bore through a pressure relief valve, and (iv) a separator piston having the mud chamber on a first side and the gas chamber on a second side; d) a ball valve rotatable between a closed position and an open position; e) an axially reciprocable piston movable between a first position and a second position, the reciprocable piston having the gas chamber positioned on a first piston side and a through bore chamber in fluid communication with the through bore positioned on a second piston side; and f) a valve rotational mechanism interconnecting the valve and the piston, wherein when the piston is in the first position the ball valve is in the closed position and when the piston is in the second position the ball valve is in the open position.
 7. The downhole shutoff valve of claim 6, wherein the reciprocable piston is exposed to the accumulator pressure on the first piston side and a through bore fluid pressure on the second piston side.
 8. The downhole shutoff valve of claim 7, wherein the reciprocable piston is the first position when the accumulator pressure exceeds the through bore fluid pressure and wherein the reciprocable piston is in the second position when the through bore fluid pressure exceeds the accumulator pressure.
 9. The downhole shutoff valve of claim 6, wherein whenever the accumulator pressure is greater than a pressure exterior to the downhole shutoff valve by a predetermined margin, a pop off valve opens and releases to the tool exterior an excess of the accumulator pressure over the pressure external to the downhole shutoff tool.
 10. The downhole shutoff valve of claim 6, further including a lockopen tool that selectably interacts with a latch groove in the through bore to position the lockopen tool in the through bore to prevent opening or closing of the valve.
 11. A downhole shutoff valve for use in a drillstring including: a) a first module having (i) a first body having a first end, a second end, and a first through bore, (ii) a flow port extending into the first body, wherein the flow port is parallel to and offset from the first through bore, and (iii) a pressure relief valve in fluid communication with the first through bore and the flow port, wherein the pressure relief valve opens when a pressure in the first through bore exceeds a pressure in the flow port by a predetermined amount; b) an accumulator module having (i) a second body having a first module end, a second module end, and a second through bore, wherein the first module end is attached to the first module, (ii) a bore extension tube connected to the first through bore at the second end of the first module and extending into the second through bore, wherein the bore extension tube has a smaller outer diameter than a diameter of the second through bore, (iii) an axially reciprocable separator piston having a first side facing the first module, the separator piston encircling the bore extension tube between an exterior surface of the bore extension tube and an interior surface of the second through bore, (iv) an accumulator charging port providing selectable communication between an exterior of the accumulator module and a gas chamber located between the second through bore and the exterior surface of the bore extension tube on a second side of the separator piston, and (v) a mud chamber in fluid communication with the flow port, the mud chamber located between the second through bore and the exterior surface of the bore extension tube on a second side of the separator piston; and c) a third module having (i) a housing attached to the accumulator module, (ii) a ball valve rotatable between a closed position and an open position, (iii) a third through bore, wherein the third through bore is coaxially aligned and in fluid communication with the first through bore and a bore of the bore extension tube, (iv) a tool bore pressure chamber in fluid communication with the third through bore, (v) an axially reciprocable piston movable between a first position and a second position, the reciprocable piston having the gas chamber positioned on a first piston side and the through bore chamber positioned on a second piston side, and (vi) a valve rotational mechanism interconnecting the valve and the reciprocable piston, wherein when the piston is in the first position the ball valve is in the closed position and when the piston is in the second position the ball valve is in the open position.
 12. The downhole shutoff valve of claim 11, wherein the gas chamber is precharged with nitrogen to create an accumulator pressure.
 13. The downhole shutoff valve of claim 12, wherein the reciprocable piston is exposed to the accumulator pressure on the first piston side and a through bore fluid pressure on the second piston side.
 14. The downhole shutoff valve of claim 11, wherein the reciprocable piston is in the first position when the accumulator pressure exceeds the through bore fluid pressure and wherein the reciprocable piston is in the second position when the through bore fluid pressure exceeds the accumulator pressure.
 15. The downhole shutoff valve of claim 11, wherein the first module further includes a pop off valve in fluid communication with the flow port.
 16. The downhole shutoff valve of claim 12, wherein whenever the accumulator pressure is greater than a pressure exterior to the downhole shutoff valve by a predetermined amount, the pop off valve opens and releases to the tool exterior an excess of the accumulator pressure over the pressure external to the downhole shutoff tool.
 17. The downhole shutoff valve of claim 11, wherein the pop off valve consists of a carrier and a poppet closed with a shear pin and opened by shearing the shear pin.
 18. The downhole shutoff valve of claim 11, wherein the first module further includes a latch groove.
 19. The downhole shutoff valve of claim 18, wherein a lockopen tool is selectably latched into the latch groove and positioned to pass through a through hole in the ball valve, thereby preventing the ball valve from rotating into the closed position.
 20. The downhole shutoff valve of claim 19, wherein the lockopen tool is selectably removable from the downhole shutoff valve to permit the ball valve to rotate between the closed position and the open position.
 21. The downhole shutoff valve of claim 11, wherein the pressure relief valve has an opening pressure less than an estimated maximum flow-induced pressure produced in the first tool bore. 